When you are about to receive head (blowjob), and shes unzips your jeans,if your jeans have been tight and you have a stiffy. The pressure is released all at once causing your hard cock to fly out and smack the ho in the face at a tremendous force.

"Dude i was totally gunna get a blowjob but then i cockpunched her. "
" I'm afraid we cannot fix your face due to the damage caused by your clients cock" - Doctor to a ho